This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
The abbreviations and terms appearing in the description and drawings are defined as below.    3GPP Third Generation Partnership Project    BS Base Station    CDMA Code Division Multiple Address    DL Downlink    DwPTS Downlink Pilot Time Slot    eNB enhanced NodeB, Base Station in E-UTRAN    E-UTRAN Evolved UTRAN    FDD Frequency Division Duplex    HO HandOver    IE Information Element    LTE-A Long Term Evolution-Advanced    MBSFN Multicast Broadcast Single Frequency Network    PDSCH Physical Downlink Shared Channel    QoS Quality of Service    RAT Radio Access Technology    RS Reference Signal    TDD Time Division Duplex    UE User Equipment    UL Up link    UTRAN Universal Terrestrial Radio Access Network
At present, sustainable development is a long-term commitment for all people in the world. This means not only development but also innovation. People should do their best to handle the resource shortage and environment deterioration. Therefore, how to improve the power efficiency and realize the power saving becomes a significant issue.
In the telecommunication area, most mobile network operators aim at decreasing the power consumption without too much impact on their network. In this case, the greenhouse emissions are reduced, while the Operating Expense (OPEX) of operators is saved.
Thus, the power efficiency in the infrastructure and terminal becomes an essential part of the cost-related requirements in network, and there is a strong need to investigate possible network energy saving solutions.
In 3GPP, Technical Report TR36.927 gives out the energy saving description. Networks may consist of LTE cells deployed as capacity enhancement, overlaying existing and optimized 2G/3G network.
FIG. 1 illustrates a scenario for Inter-RAT energy saving. As shown in FIG. 1, E-UTRAN Cells 103, for example, Cell C 103C, Cell D 103D, Cell E 103E, Cell F 103F, and Cell G 103G, are totally covered by the same legacy RAT Cell A 101 and B 102 (e.g. UMTS or GSM). Cell A 101 and Cell B 102 have been deployed to provide basic coverage of the services in the area, while other E-UTRAN cells 103C-103G boost the capacity. The LTE cells, e.g., 103C-1036 could be controlled on/off according to some operator's policy, such that the energy may be saved.
FIG. 2 illustrates a scenario for Inter-eNB energy saving. As shown in FIG. 2, E-UTRAN Cells 203, for example Cell C 203C, Cell D 203D, Cell E 203E, Cell F 203F and Cell G 2036, are covered by the E-UTRAN Cell A 201 and B 202. Here, Cell A 201 and Cell B 202 have been deployed to provide basic coverage, while the other E-UTRAN cells 203C-203G boost the capacity. When some cells providing additional capacity are no longer needed, they may be switched off for energy optimization. In this case, both the continuity of LTE coverage and service QoS is guaranteed.
TR 36.927 also describes solutions for Intra-eNB energy saving. A single cell can operate in an energy saving mode when the resource utilization is sufficiently low. In this case, the reduction of energy consumption will be mainly based on traffic monitoring with regard to QoS and coverage assurance. In the protocol, Intra-eNB energy saving has two approaches:
1. Configuring MBSFN Subframes
MBSFN subframes have less common reference signals (CRS) than normal subframes, and hence configuring as much as possible MBSFN subframes allows reduced eNB transmission time.
2. Configuring DwPTS in Special Subframe.
For TDD, the special subframe consists of three parts, i.e. DwPTS, Guard Period and UpPTS. The length of each part is configurable. To configure the DwPTS of subframe 1 and 6 (if applicable) to the minimum length (3 OFDM symbols) can result in a subframe similar to an MBSFN subframe.
Another method for energy saving is called adaptive TDD. Different TDD DL/UL configurations consume different energy. The adaptive TDD comprises changing the TDD DL/UL configuration when operator's policy met.
However, the above mentioned Inter-RAT and Inter-eNB energy saving only consider cell level, which means to active or deactive an entire cell. Intra-eNB only consider energy saving within an eNB, but not coordinate within the network, which may generate big impact to the network, such as interference between DL and UL, lost measure object, etc.
Furthermore, the method of configuring MBSFN subframe still needs sending Reference Signal, and thus limited energy may be saved. The method of configuring DwPTS can only save a little energy, because the DwPTS consumes a small amount of energy overhead. The adaptive TDD could only be used for TDD, and could lead extra interference.